Air- and water-stable hydrophobic ionic liquids N-alkylpyridinium bis(trifluoromethylsulfonyl)imide ([C(n)py][NTf2], n = 3, 6) were synthesized. The density, surface tension, dynamic viscosity, and electrical conductivity of [C(6)py][NTf2] were measured in the range of T = (283.15 to 338.15) K. The density, dynamic viscosity, and electrical conductivity of [C(3)py][NTf2] were measured in the range of T = (308.15 to 338.15) K. The melting and glass transition temperatures of the two ILs were determined according to the differential scanning calorimetry (DSC). The physicochemical properties, including molecular volume, standard molar entropy, lattice energy, parachor, molar enthalpy of vaporization, interstice volume, interstice fraction, and thermal expansion coefficient, were estimated in terms of empirical and semiempirical equations, as well as the interstice model theory on the base of the experimental values. The dynamic viscosity and electrical conductivity values were fitted by Vogel-Fulcher-Tammann (VFT) and Arrhenius equations for [C(6)py][NTf2] and the Arrhenius equation for [C(3)py][NTE2].